Most conventional techniques for developing latent fingerprints depend on the presence of oil from the donor’s skin left behind on the surface where the print is found. Over time, the oil dries, evaporates, or is worn or washed away, making the print difficult to see with powders and cyanoacrylate (superglue) fuming techniques. New research from Australia describes a process where prints up to a year old can be developed on a non-porous surface, using the amino acids left behind by the donor.
This research comes from the University of Technology in Sydney, NSW Australia. The process has three steps. First, the surface where the prints are believed to be present is immersed in a solution of anti-L-amino acid antibodies conjugated to gold-citrate nanoparticles in a water-acetone mixture, and incubated for 30 minutes at 37°C (99°F). The surface is washed, then a second solution of anti-rabbit secondary antibody labeled with Fluorescent Red 610 is applied at room temperature for 15 minutes, then washed again. Finally, the developed prints are illuminated and visualized with a xenon arc lamp emitting a wavelength of 590 nm, and viewed with a 650 nm bandpass barrier filter.
While that sounds like a production that could be completed only in a sophisticated laboratory, it’s likely that a commercialized process would furnish the necessary reagents, light and filters in a kit with labels something like “Solution A” and “Solution B.”
Latent fingerprints are left behind when we touch something because of the mixture of water, fatty acids, salts and free amino acids on our fingertips. Most latent print development techniques target the oily secretions from the sebaceous glands associated with hair follicles in our skin. These oils will be present only if the friction ridges have touched a hair-covered area of the body prior to contacting the surface holding the latent print. Amino acids on the skin surface originate in the eccrine (sweat) glands distributed across the palms of the hands and the soles of the feet, and are therefore present on friction ridges whether they have come into contact with hair follicles or not.
Conventional methods, such as dusting with lampblack powder or cyanoacrylate fuming, work well on non-porous surfaces when the prints are fresh. As the prints age, development with these methods produces progressively less detail with more background staining. The antibody technique, which targets the amino acids in a latent print, doesn’t seem to be affected by aging of the prints. Latent prints up to a year old have been developed with this method, indicating that the amino acid deposit from the prints is chemically stable on most non-porous surfaces.
There is another sophisticated development technique that targets blood group antigens present on some friction ridges, but it is limited to 80 percent of the population. The other 20 percent do not secrete blood type carbohydrates necessary for the process in their perspiration.
A quirk of this new amino acid antibody process is that it is especially effective with print donors who regularly consume soft drinks, chewing gum or other substances containing phenylalanine-based sweeteners, such as aspartame (NutraSweet). Consumption of this food additive increases the level of phenylalanine in fingerprint secretions, and phenylalanine produces an immune response to the anti-L-amino antibodies.
Spindler, X., Hofstetter, O, McDonagh, A., Roux, C and Lennard, C. Enhancement of latent fingermarks using anti-L-amino antibodies conjugated to gold nanoparticles. Chem. Commun., 2011, 47, 5602-5604.